Correction: Emerging investigator series: a holistic approach to multicomponent EXAFS: Sr and Cs complexation in clayey soils.

Correction for 'Emerging investigator series: a holistic approach to multicomponent EXAFS: Sr and Cs complexation in clayey soils' by Pieter Bots et al., Environ. Sci.: Processes Impacts, 2021, DOI: .

Emerging investigator series: a holistic approach to multicomponent EXAFS: Sr and Cs complexation in clayey soils.

Strontium and caesium are fission products of concern at many nuclear legacy sites and Cs is additionally a significant consideration at sites in the aftermath of nuclear accidents and incidents. Such sites require long-term management to minimize the risk of such contaminants to the environment and the public. Understanding the geochemical speciation of Sr and Cs in situ in the soils and groundwater is essential to develop engineered management strategies. Here we developed and utilized a comprehensive approach to fitting the EXAFS of Sr and Cs adsorption to single mineral phases and a composite clayey soil. First, a shell-by-shell fitting strategy enabled us to determine that Sr surface complexes involve the formation of bidentate edge sharing complexes with anatase and illite-smectite, and form at the silicon vacancy sites at the kaolinite basal surfaces. Cs surface complexes form at the silicon vacancy sites at the illite-smectite and kaolinite basal surfaces. Second, using a subsequent holistic approach we determined the predominance of these complexes within a composite clayey soil. Sr was dominated by complexation with illite-smectite (72-76%) and to a lesser extent with kaolinite (25-30%) with negligible complexation with anatase, while Cs complexed roughly equally to both illite-smectite and kaolinite. The presented approach to fitting EXAFS spectra will strengthen predictive modelling on the behaviour of elements of interest. For example, the details on Sr and Cs speciation will enable predictive modelling to characterise their long-term behaviour and the design and validation of evidence-based engineering options for long-term management of nuclear legacy sites.

Scavenged 239Pu, 240Pu, and 241Am from snowfalls in the atmosphere settling on Mt. Zugspitze in 2014, 2015 and 2016.

Concentrations of 239Pu, 240Pu, and 241Am, and atomic ratio of 240Pu/239Pu in freshly fallen snow on Mt. Zugspitze collected in 2014, 2015 and 2016 were determined by accelerator mass spectrometry (AMS). For the sub-femtogram (10-15 g) - level of Pu and Am analysis, a chemical separation procedure combined with AMS was improved and an excellent overall efficiency of about 10-4 was achieved. The concentration of 239Pu ranges from 75 ± 13 ag/kg to 2823 ± 84 ag/kg, of 240Pu from 20.6 ± 5.2 to 601 ± 21 ag/kg, and of 241Am was found in the range of 16.7 ± 5.0-218.8 ± 8.9 ag/kg. Atomic ratios of 240Pu/239Pu for most samples are comparable to the fallout in middle Europe. One exceptional sample shows a higher Pu concentration. High airborne dust concentration, wind directions, high Cs concentrations and the activity ratio of 239+240Pu/137Cs lead to the conclusion that the sample was influenced by Pu in Saharan dust transported to Mt. Zugspitze.

Spectroscopic identification of binary and ternary surface complexes of Np(V) on gibbsite.

For the first time, detailed molecular information on the Np(V) sorption species on amorphous Al(OH)3 and crystalline gibbsite was obtained by in situ time-resolved Attenuated Total Reflection Fourier-Transform Infrared (ATR FT-IR) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The results consistently demonstrate the formation of mononuclear inner sphere complexes of the NpO2(+) ion irrespective of the prevailing atmospheric condition. The impact of the presence of atmospheric equivalent added carbonate on the speciation in solution and on the surfaces becomes evident from vibrational data. While the 1:1 aqueous carbonato species (NpO2CO3(-)) was found to become predominant in the circumneutral pH range, it is most likely that this species is sorbed onto the gibbsite surface as a ternary inner sphere surface complex where the NpO2(+) moiety is directly coordinated to the functional groups of the gibbsite's surface. These findings are corroborated by results obtained from EXAFS spectroscopy providing further evidence for a bidentate coordination of the Np(V) ion on amorphous Al(OH)3. The identification of the Np(V) surface species on gibbsite constitutes a basic finding for a comprehensive description of the dissemination of neptunium in groundwater systems.

Structural characterization of the aqueous dimeric uranium(VI) species: (UO2)2CO3(OH)3-.

A combined theoretical and spectroscopic approach was used to refine structural data of the aqueous dimeric U(VI) species, (UO2)2CO3(OH)3(-). Several isomer structures of this complex were already derived from previous X-ray absorption and NMR experiments (Szabó, Z. et al., J. Chem. Soc., Dalton Trans., 2000, 3158-3161) but due to unequivocal results a distinct structure could not be determined and uncertainties remain. In this work, the Gibbs energies and U-U distances obtained from density functional theory (DFT) calculations predict two isomers, one with a carbonate ligand and one with two hydroxo groups as bridging groups, as most likely structures. The experimental IR spectrum indicates a bidentate coordination of the carbonate ion and the presence of two spectroscopically specifiable uranyl moieties as it is also predicted by the spectra computed on the base of DFT. Taken together theoretical and experimental results the isomer with a carbonate ligand bridging the two uranyl units appears most likely to represent the predominant structure. Contributions to a small extent of an isomer with a non-bridging carbonate anion cannot be completely ruled out.